I want to lighten up my kit for Sierra Nevada winter camping. In my opinion, snow caves take too long to build and you get wet. Some of my colleagues doubt whether silnylon when supported over the trench by 2 ski poles is strong enough and are recommending that I stick with the classic hardware store (polyester?) blue tarp. Does anyone have practical experience with using for example the 5X8 ID tarp when expecting 6 to 20 inches of snow to fall during the night?

First of all, if you are getting wet when digging a snow cave, you are doing something wrong. The standard uniform is nothing but a polypro base layer, and then Gore-tex or equivalent over it. No insulation, or else you'll get very hot.
Suppose that you dig a standard snow trench. How would you use those poles? If you just lay them flat across the trench and then lay a tarp over, that will begin to work, but it might also collapse if you get enough snow weight on it. Once you've used it, it becomes very hard to excavate the poles out again. Not recommended.
The standard shelter method is to use a snow saw and cut blocks from a hard flat snow surface. Roughly 16" cubes should do it. Cut and remove the blocks in a square pattern, perhaps growing to 8'x8'. Once you've removed one layer of blocks, you might be removing a second layer also. As each block is removed, it is placed around the outside of the 8'x8' square, producing a wind wall. The wind wall ends up being one or two layers high, and you've dug down one or two layers. You use X-C skis, ski poles, fiberglas poles, or whatever to construct an arch over the top layer of the wind wall, and cover that with a Megamid or tarp or whatever you have that is large enough, and anchor down the corners and edges. One leeward corner of the wind wall is excavated to be the door. There should be enough room for about four people to sleep. Tried and true.
--B.G.--

Sorry Bob, but I have to disagree with you about 'if you're getting wet when digging a snow cave you're doing it wrong' statement.

When digging a snow cave you're going to get wet from the snow (and the higher humidity inside the cave) regardless of how much clothing you're wearing. I personally like to wear a thin base layer and a thin soft shell when digging out a snow cave or quinsy.

As far as using a silnylon tarp as a cover for a snow trench; I don’t see any issues with doing so. Using silnylon tarp as a cover for a snow trench can be great when you don’t have dense snow for cutting blocks to build a roof. I for one have used a Id 5’x8’ tarp as a cover for a snow trench many times in high snowfall without issue. Typically when I use the tarp to cover a snow trench I set the tarp up in a lean to configuration with each side of the tarp supported by the snow. Keep in mind though that you will need to clear off the snow from your tarp every so often during heavy snow fall.

Edited by chadnsc on 01/22/2010 07:06:10 MST.

Chad, you are entitled to your opinions, even if they are wrong. (g)
Two things. First, I suspect that you are younger than some of us, and you are able to work faster and generate more heat, so your results are different. Also, I suspect that the nature of your Minnesota snow is a lot different from my California snow.
--B.G.--

> Some of my colleagues doubt whether silnylon when supported over the trench
> by 2 ski poles is strong enough and are recommending that I stick with the classic
> hardware store (polyester?) blue tarp.

Absolutely classic reaction from traditional heavy-weight walkers to anything light-weight. Do not try to change what they do, just look after your own load.

Cheers

Silnylon will work great as a trench cover as long as you
allow for any snow loads in your design.

Young or old, dry or wet snow. I have never been able to stay
dry while building a snow cave. I just plan on having a change
of long underwear in my layering system.

Bill,

I'm not sure how long you have been building snow shelters or how many you have built so you may be more experienced than me. However in the three years and 20 plus shelters I've built I have found that it becomes rather humid inside the snow cave during construction and that you will experience dampness from the snow and humidity.

It is because of that that I disagree with you that you will not get wet or damp when building a snow shelter. I agree that you should be wearing as little of clothing as possible with some type of soft shell jacket to keep dry when digging out a snow cave.

I’m not trying to belittle you Bill as your advice in this subject is quite welcome and very helpful. I only suggest that you try not to speak in absolutes when it comes to subjects like this (we’ve all done it sometime) where location, physical fitness, and personal techniques can affect the outcome.

Take care!

Edited by chadnsc on 01/23/2010 18:54:18 MST.

Silnylon should be plenty strong. Two tips - one is, you need to pull it taut. So if you are going to use your poles and skis as rafters, you 'll want some good snow stakes for the tarp. Second tip is, slope the thing. dig you trench aross a slope, so one side is higher than the other. Pack some snow onto the high side of the tarp to seal it to the snow, and get it taut. That way, snow will slide off easier, and if if starts to pile up you'll be able to knock it off from the inside more easily with a whack or two.
Oh, and one more thing - think about something for a door to your trench - if it snows hard, you need more than a roof. One way is to have a piece of silnylon with a sleeve sewn into one edge - slide your ski pole through the sleeve and set that at the open end of the trench, so the fabric hangs down over the doorway. Might need some stake loops so you can secure the bottom.
All that said, I wouldn't bother. Get a BD Betalight instead and skip most of the digging.

What about Cuben Fiber? Would that be suitable?

In my experience, whenever you use a tarp in the snow, or tent for that matter, and you expect heavy snow. You will have to wake up to remove snow from the top of the shelter.